1. Field of the Invention
This invention relates to the accurate placement of central venous catheters within a central venous compartment of the body, and more particularly to novel techniques described herein employing venous oximetry to facilitate such accurate placement.
2. Background Information
Central venous catheters (CVCs) are placed in excess of ten million times annually in the United States. Access to the central venous compartment (e.g. Great veins interconnected to the cardiopulmonary system) by such CVCs is acquired to allow for the administration of fluids, nutritional support and medications that are not necessarily suitable for peripheral venous delivery. CVCs may also be employed to access the central venous compartment to enable measurement of certain hemodynamic variables that are otherwise unobtainable by accessing peripheral veins, or by non-invasive techniques.
There are certain risks associated with the insertion of CVCs, which include pneumothorax (the collection of gas in the space surrounding the lungs), hemothorax (the collection of blood/fluid in that space), failed insertion and inadvertent arterial puncture. Where a CVC is inserted via an internal jugular venous approach, the most commonly described, and very dangerous, complication is inadvertent carotid artery puncture. This is the second most commonly described complication in the subclavian venous approach.
There are several current approaches to percutaneous CVC placement. In Seldinger's Method, the skin is prepped, and under sterile conditions, the percutaneous vein is punctured with a thin needle (for example, 20-gauge, or approximately 1 mm in outer diameter). A flexible guide wire is then introduced through the needle lumen and the needle is removed. A larger diameter dilator is then guided over the wire to facilitate passage of a larger bore (for example, 8-9 French, or up to approximately 3-4 mm in outer diameter). An alternate insertion approach entails venipuncture by the thin needle followed by guidewire placement. The larger-diameter catheter is then inserted while the guide wire is removed. Other approaches may also be employed, depending upon the type of device being inserted. Each of these approaches requires perforation of the target vessel using a needle.
While inadvertent arterial puncture using the introducing needle is usually an obvious condition, because of the arterial bleeding that results from even a small puncture, it often is not. Subsequent placement of a large-bore catheter or introducer into the carotid artery or another arterial structure can have lethal consequences. There have been reports of thromboembolic sequelae (broken blood clots leading to stroke, embolism, etc.) as a result of such punctures. Once damage has occurred, the neck or other region may require surgical exploration to assess and repair the damage. This can lead to further risk, expense and delays in attending the initial surgical problem which necessitated the CVC insertion.
One approach to reducing the risk in placing a percutaneous CVC is to monitor the insertion using interoperative imaging with an ultrasound or another type of internal imaging device. In some situations, radiopaque markers on the catheter/needle can be employed to assist guidance under fluoroscopy or similar scanning techniques. However, the surrounding structures of the neck may obscure a clear view of the target vein. Thus, while the needle appears clearly, the walls of the vein may not. Hence, reports of inadvertent carotid artery puncture, subsequent arterial cannulation and morbidity persist, even when employing interoperative imaging.
Another possible approach to reducing the risk of arterial cannulation is to employ a scout needle, in which a short, 20-gauge catheter is operatively connected by a pressure line to a pressure transducer before insertion of a guidewire. A predetermined variation or differential in pressure may indicate arterial cannulation. However, this approach entails several additional steps to connect and disconnect the needle's pressure line to a bedside transducer/display. This approach also requires additional manipulation and increase the chance that the catheter will become “extra-vascular.” Also, the requirement for specialized pressure monitoring equipment adds cost and complexity to the procedure, and such equipment is not always available to the practitioner.
A technique that more reliably ensures the needle is in communication with the vein, and not an artery is highly desirable.